One Time Fly-in Ad Cookie

Hey all, I have a fly-in ad on my site that shows on internet explorer browsers on page exit via the unload atribute.

Problem is the software I use to create the code is weak, and it makes the flyin show up every single time a page is loaded.

I need a quick fix to make it drop a cookie and the proper code to make it find the cookie and show up only once per session.

Thanks,

you must be in Internet explorer to view the fly-in you can see an example here: Job Description for Cashier